1. Field of the Invention
The present invention relates to a switching regulator that converts an input voltage inputted to an input terminal into a predetermined constant voltage and that outputs the constant voltage to a load from an output terminal.
2. Description of the Related Art
In recent years, a non-insulated type switching regulator that includes an inductor is used as a highly-efficient power source circuit used for a small electronic apparatus.
As a control method of the switching regulator, two schemes are known. One scheme is PWM (Pulse Width Modulation) control in which output voltage is controlled to be constant by changing a duty cycle of a clock pulse of a constant cycle. Another one is PFM (Pulse Frequency Modulation) control in which output voltage is controlled to be constant by changing a cycle of a clock while keeping pulse width constant.
In the PWM control, since On/Off control is performed on a switching transistor at constant period even for a light load, efficiency for a light load for which output current is small becomes deteriorated. On the other hand, according to PFM control, since the frequency of the signal for controlling the switching transistor changes according to a connected load, PFM control is more efficient than PWM control for light loads.
Therefore, there is a switching regulator that switches between PWM control and PFM control. A switching regulator that performs control by switching between PWM control and PFM control is described in Japanese Laid-Open Patent Application No. 2009-278713, for example.
Such a switching regulator includes an amplifier for PWM control and an amplifier for PFM control so as to realize PWM control and PFM control by switching between the amplifiers.
In the configuration of the switching regulator, there are problems in that there is variation of output voltages between control modes and that the circuit size becomes large.